Factors Affecting SPT

Drugs

Middleton 7th Ed.

Drugs	Suppression			Note
	Degree	Duration (days)	Drug affects SPT?
H1 antihistamines
Azelastine (intranasal)	++++	3–10 days-----	Yes	A single dose of azelastine nasal spray does not significantly alter response to histamine, but if multiple doses are used it should be discontinued for at ≥48 hours.
Cetirizine	++++	3–10 days	Yes
Chlorpheniramine	++	1–3 days	Yes
Cyproheptadine	0 to +	1–8 days	Yes
Desloratadine	++++	3–10 days	Yes
Diphenhydramine	0 to +	1–3 days	Yes
Doxepin	++	3–11 days	Yes	Topical doxepin has been shown to abolish skin reactivity after 1–3 days of therapy and for up to 11 days after discontinuation.
Hydroxyzine	+++	1–10 days	Yes
Ketotifen	++++	>5 days	Yes
Levocetirizine	++++	3–10 days	Yes
Loratadine	++++	3–10 days	Yes
Olopatadine (ocular)	0		No	In a small study, 7-10 day treatment with olopatadine 0.2% (Pataday is 0.2% , Patanol is 0.1%) did not suppress wheal and flare areas during allergy testing, and discontinuation for skin-prick testing did not appear to be necessary. Alcon: Pataday is not expected to interfere with the results of allergen skin testing as the low blood level of drug expected to occur following the usual topical ophthalmic dose should not produce a systemic effect.
Promethazine	++	1–3 days	Yes
H2 antihistamines				Discontinuation of H2 antagonists on the day of testing is probably sufficient to prevent significant suppression of skin tests.
Cimetidine	0 to +		No
Ranitidine	+		No
Psychiatric Medications
Imipramines	++++	>10 days	Yes	TCAs exert a potent and sustained reduction in skin responses to histamine that may last for a few weeks.
Phenothiazines	++		Yes	Tranquilizers and antiemetic agents of the phenothiazine class have H1 antihistaminic activity and can abrogate skin test responses.
Antipsychotic (typical and atypical)			Maybe	Many have high histamine H1 receptor affinity, particularly clozapine, olanzapine, chlorpromazine, loxapine, perphenazine, quetiapine, risperidone, aripiprazole (see table below).
Corticosteroids
Systemic, short term	0			Short-term (<1 week) corticosteroids in asthmatic patients does not modify the cutaneous reactivity to histamine or allergen.
Systemic, long term	Possible		Yes	Long-term corticosteroid therapy does not alter histamine-induced reactivity in skin, but affects cutaneous mast cell responses and modifies skin texture, making interpretation of immediate skin tests difficult in some cases. It has been shown that allergen-induce skin tests can be accurately performed in asthmatic patients receiving long-term oral corticosteroid treatment.
Inhaled	0			As normal doses of ICS produce fewer systemic effects than oral steroids, their potential for interference is predictably insignificant.
Topical skin	0 to ++		Yes	Topical corticosteroids for a period of 1 week reduces both the immediate- and the late-phase skin reaction induced by allergen.
Other Allergy Medications
Pimecrolimus, topical	0		No
Theophylline	0 to +		No	Theophylline slightly reduces skin tests but its administration does not need to be stopped prior to testing.
Cromolyn	0			Inhaled cromolyn and nedocromil do not alter the whealing response to skin tests with allergens or degranulating agents.
Montelukast	0			One study showed that montelukast given for 5 days suppressed the itching and flare response from skin prick tests but not the wheal size.
Specific immunotherapy-----	0 to ++		No
Adrenergic receptor medications
Beta2 agonists (inhaled short-acting)	0 to +		No	Short-acting inhaled β2 agonists in doses approved for the treatment of asthma do not usually inhibit allergen-induced skin tests.
Beta2 agonists (PO/IV short-acting)	0 to ++		No
Formoterol (inhaled)	Unknown-----
Salmeterol (inhaled)	Unknown
Propranolol				β-blocking agents such as propranolol can significantly increase skin histamine reactivity.
Dopamine	+
Clonidine	++

Note

• Beta blockers -β-blocking agents such as propranolol can significantly increase skin histamine reactivity.
• Angiotensin-converting enzyme (ACE) inhibitors moderately increase skin reactivity to allergen and histamine.

Antipsychotic H1 Receptor Binding Affinitiy

(Lower Ki = higher affinity)

Rhinitis Practice Parameter 2008

Allergy Diagnostic Testing Practice Parameter 2008

Shah 2011

Herbal Supplements

Allergen extract potency

• Allergen quality and potency; amount of allergen in the extract.
• Some extracts (e.g., Hymenoptera venoms) can induce false-positive reactions by non-immunologic mechanisms.
• Preservatives in extracts may be irritative: sodium merthiolate can elicit a wheal-and-flare reaction in non-sensitized subjects.

Area of the body

• Back
  • The mid and upper back areas are more reactive than the lower back.
  • The back as a whole is more reactive (about +20%) than the forearm
• Arms
  • The antecubital fossa is the most reactive portion of the arm; wrist is the least reactive.
  • The ulnar side of the arm is more reactive than the radial.
  • Recommended that tests should not be placed in areas 5 cm from the wrist or 3 cm from the antecubital fossae.

Age

• Infants react predominantly with a large erythematous flare and a small wheal.
• It is possible to perform SPT in infancy, but the size of the wheal is often reduced, and criteria of positivity should always compare the size of the wheal induced by allergen with histamine and negative control.
• Skin reactivity has been demonstrated to be reduced in infants (<12 to 18 months of age) and the elderly.
• Skin test wheals increase in size from infancy to adulthood and then often decline after the age of 50.

Race

• The whealing capacity to histamine is greater in healthy non-atopic black subjects with darkly pigmented skin than it is in whites with light skin pigmentation.

Pollen Season

• Skin sensitivity for tree pollen allergy increases after the pollen season and then declines until the next season. This may be relevant in patients with a low level of sensitization for allergen extracts that have weak potency.
• UV-B radiation significantly reduces wheal intensities.

Comorbidities

• Stress - in one study, the addition of stress led to the conversion of SPTs from negative to positive
• Eczema - may diminish skin reactivity to histamine but this is not consistently observed.
• Chronic renal failure/regular hemodialysis treatment - usually have a reduced skin reactivity and the texture of their skin makes testing difficult.
• Cancer - may have reduced skin reactivity more pronounced on the flare than on the wheal.
• Spinal cord injuries or peripheral nerve abnormalities (e.g. diabetic neuropathy) - reduced flare reactivity.

Non-factors

• Circadian variation - minimal and does not affect interpretation of skin tests.
• Gender - no clear-cut differences noted.
  • There may be a higher prick test response to histamine in male rather than female subjects.
  • Women displayed the weakest histamine whealing capacity during the first day of the menstrual cycle and a second minimum around the 20th day, and the strongest allergen whealing capacity at mid-cycle.

References